1. Field of the Invention
The present invention is directed to supported organometallic catalysts and catalyst compositions useful in the oligomerization and polymerization of 1-olefins alone or in combination with functionalized olefins or cyclic olefins.
2. Background of the Invention
Ziegler-Natta coordination-type compounds, chromium compounds, other early transition metal compounds, as well as free-radical type of initiators have been used to catalyze the (co)polymerization of ethylene. In certain instances, catalysts alone or with an activator (e.g., trialkylaluminum) have been used with a support material such as an inorganic oxide (e.g., silica). In such instances, the catalyst is either coated on or impregnated in the support material. The commercial use of silica as a support for Ziegler-Natta catalysts is described in, for example, Macromol. Symp., 1995, 89, 563.
Over the past decade, single-site catalyst systems for olefin polymerizations have been developed. These systems typically use a Group IV-B metallocene (i.e., a compound having at least one substituted or unsubstituted cyclodienyl group coordinated to a transition metal by a .pi. bond) and a non-coordinating ionic activator (e.g., methylaluminoxane).
Such homogeneous catalyst systems generally are most suitable when used in solution polymerization processes where they provide polymers of high bulk density with good productivity. However, slurry and gas phase polymerization processes sometimes are preferred; slurry processes combine the advantages of homogeneous catalysis with the ease of particle formation and low viscosity, whereas gas phase systems alleviate the need for use and removal of a liquid reaction medium.
Catalyst compositions useful in homogeneous polymerization processes are known to have only limited utility in slurry and gas phase processes. Catalyst compositions typically used in homogenous polymerizations tend to cause reactor fouling, poor productivity, poor polymer bulk density, and poor polymer particle morphology when used in slurry processes. In the hope of overcoming these limitations, supported catalyst systems have been developed for slurry and gas phase polymerization.
One type of conventional supported catalyst system involves modifying a support with an alkylaluminum reagent followed by impregnation with a metallocene catalyst and solvent removal. However, when a catalyst merely is coated on or impregnated in a supported material, it tends to release from the support during slurry polymerizations, resulting in the same detrimental results stated above. Thus, supported catalyst systems which do not permit the catalyst to dissolve and be carried into the reaction medium are highly desirable.
Several relatively recent teachings have disclosed the use of silica-supported metallocene/partially hydrolyzed aluminumalkyl activated systems for slurry and gas phase heterogeneous olefin polymerization processes. However, these systems, like others which use methylaluminoxane (MAO) and the like as activator, have known disadvantages of requiring high molar ratios of aluminum to metallocene to achieve a catalyst composition of suitable reactivity. In addition, such systems still produce undesirable low molecular weight polymer product.
Others have proposed using certain polyanionic transition metal catalyst compositions in which the anionic moiety is composed of a plurality of metal or metalloid atom-containing, non-coordinating anionic groups that are chemically bonded to a support component (e.g., silica) through a hydrocarbyl moiety. These catalyst systems have been found to have certain disadvantages, however. First, the anionic metal or metalloid component-modified support substrate is bonded to the catalyst by ionic bonding and requires the catalyst to provide the cationic moiety. Such bonds can permit release (resolubilization) of the catalyst, especially in slurry processes. Also, due to the catalyst's metal atom providing the cationic polymerization center as well as serving as the counterion for ionic bonding, catalytic activity can be reduced. Further, it is known that the support should be made substantially free of residual hydroxyl groups as such groups are known to reduce the activity of the intended catalyst. However, the required removal of all such groups is very difficult. Still further, exposure of such a catalyst to high concentrations of functional groups (especially oxygen-containing groups) can poison the catalyst system. Additionally, such catalyst systems have low catalytic activity, are sensitive to oxygen and oxygen containing-compounds, and provide polymer products having low polydispersity (i.e., a narrow molecular weight distribution). Polymer products having low polydispersity are difficult to process (e.g., extrude) by known techniques.
WO 98/42664 and WO 98/2665 describe non-ionic, late transition metal catalysts that are substantially non-oxophilic and contain bidentate ligands. These catalysts are described as useful to form linear homopolymers of 1-olefins as well as copolymers of 1-olefins, cyclic olefins, and functionalized olefins (monomers having oxygen atom-containing groups such as ether, ester, hydroxyl, carboxyl, etc., groups). Although such catalysts may be applied to a support, they generally are used in homogeneous catalyst systems.
Providing a supported non-ionic catalyst useful in slurry and heterogeneous gas phase polymerization processes is highly desirable. Further, providing neutral catalyst compositions that are covalently bonded to the support and, thereby, substantially inhibiting the catalyst moiety from releasing into the reaction medium also is desirable. Finally, providing a supported catalyst that can be used in slurry or gas phase polymerization processes without concern for the presence of oxygenated organic material within the system and/or as part of the olefinic monomer feedstock(s) also remains desirable.